1. Field of the Invention
The present invention relates to a flexible tube for an endoscope.
2. Description of the Prior Art
Generally, a flexible tube for an endoscope has a structure which includes a tubular core obtained by covering the outer periphery of a spiral tube with a mesh tube and an outer cover formed of a synthetic resin or the like and provided over the outer periphery of the tubular core.
In endoscopic examination, the flexible tube for an endoscope is inserted along the body cavity to a deep part such as the stomach, duodenum, small intestine, and large intestine. In order to perform the inserting operation easily and reliably, it is necessary for the flexible tube that a push-in force applied to the proximal end (side closer to the operator) of the flexible tube is fully transmitted to its distal end. However, if buckling occurs in the flexible tube, the push-in force can not be fully transmitted to the distal end because the push-in force is partially absorbed by the bent part where the buckling occurs. This means that such a flexible tube for an endoscope can not achieve reliable inserting operation. In order to avoid the occurrence of such buckling, it is necessary for the flexible tube to have sufficient flexibility so that bending is hard to occur. Further, the outer cover must be firmly attached or bonded to the tubular core since buckling is liable to occur at areas where the outer cover is peeled off from the tubular core.
Furthermore, in order to perform the inserting operation reliably, it is also necessary for the flexible tube that a rotational force (that is, a twist) applied to the proximal end thereof is fully transmitted to the distal end thereof. In other words, a flexible tube for an endoscope is also required to have satisfactory rotational followability.
Moreover, a flexible tube for an endoscope is also required to have a relatively high stiffness on the proximal end side (side closer to the operator) and have a flexibility on the distal end side from the viewpoint of the operability and safety of insertion and reduction in the burden on the patient.
Up to now, there are known several flexible tubes for an endoscope which aim to improve the insertion operability in view of the problems described above. One of such flexible tubes is disclosed in Japanese Laid-open Patent Applications No. Hei 5-50287, in which an outer cover of a flexible tube for an endoscope is constructed from a double layer structure comprised of an outer layer made of a material having good elasticity and an inner layer made of a material having good resiliency, thereby improving resiliency of the flexible tube as a whole. Other example of such flexible tube is disclosed in Japanese Patent No. 2641789, in which a distal end side of the flexible tube is made of a soft elastomer and a proximal end side thereof is made of a hard elastomer so that the stiffness varies from the distal end side toward the proximal end side.
However, in these prior arts described in the above, the bonding force between the outer cover and the core has been left out of consideration, so that there is a case that the outer cover is peeled off from the core after repeated use, thus leading to the deterioration in flexibility and resistance to buckling of the flexible tube. In short, there is a problem in the durability of the flexible tube for an endoscope.
Furthermore, although an endoscope must be cleaned and disinfected every time when it is used, in the above prior arts no consideration is given to the chemical resistance of the outer covers. Consequently, in these prior arts, deterioration proceeds during the repeated disinfections, which results in possibility of generation of fine cracks or the like and peeling off of the outer cover from the core.